Surface protective film

Abstract

The present specification relates to a surface protective film which has an indentation depth of 3.0 [mu] m or more as measured by a specific method, and which can minimize a wafer non-separation rate.

Description

TECHNICAL FIELD

[0001] The present application relates to a surface protection film, and more particularly, to a surface protection film for reducing a non-separation rate in a stealth dicing operation in the semiconductor field.

[0002] This application claims priority to and the benefit of Korean Patent Application Nos. 10-2023-0139225 and 10-2024-0015148, filed on October 18, 2023 and January 31, 2024, respectively, with the Korean Intellectual Property Office, the contents of which are incorporated herein by reference in their entirety. BACKGROUND

[0003] The surface protection film is a multi-layer stack including a base film, an adhesive film, etc., and is a film for protecting a wafer in a semiconductor wafer processing process.

[0004] Specifically, during a processing process of a semiconductor wafer, a surface protection sheet is attached to prevent damage to a surface on which a circuit is formed in a backgrinding process on the surface on which the circuit is formed.

[0005] However, a stealth dicing process is applied before a backgrinding process, and the stealth dicing process is an operation in which a crack (separation) occurs in a stealth dicing area when the backgrinding process is applied, so that the wafer is singulated into a single chip.

[0006] However, as the thickness of the wafer becomes thinner and the circuit surface becomes more complex, there is a problem of a high non-separation rate due to chips not being singulated.

[0007] Therefore, research is needed to solve the above problems. SUMMARY

[0008] TECHNICAL PROBLEM

[0009] To solve the above problems, the present inventors found that the reduction of the non-separation rate can be determined in advance by applying nanoindentation technology to the adhesive film of the surface protection film, thereby determining that the method developed based on this finding can effectively reduce the non-separation rate when the indentation depth is 3.0 µm or more under certain conditions.

[0010] Therefore, the present specification aims to provide a surface protection film applying the above features.

[0011] TECHNICAL SOLUTION

[0012] One exemplary embodiment of the present specification provides a surface protection film including: a base film; and an adhesive film on one surface of the base film, wherein the adhesive film has an indentation depth of 3.0 µm or more as measured by the following Method 1.

[0013] [Method 1]

[0014] The indentation depth means the depth measured when, in a state in which a glass substrate is provided on the surface of the base film opposite to the surface in contact with the adhesive film, a nanoindenter provided with a semispherical ball tip having a diameter of 2 mm at one end is used to apply a force of 5 mN to the adhesive film at an indentation speed of 0.25 mN / sec, and then the force of 5 mN is maintained for 5 seconds.

[0015] Advantages

[0016] The surface protection film according to the exemplary embodiment of the present application provides the advantage of significantly reducing the non-separation rate to minimize defects. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 and Figure 2 Each shows a schematic view of a surface protection film.

[0018] Figures 3 to 5 Each is a schematic view of a mechanism in which separation occurs during polishing.

[0019] 1: negative current collector

[0020] 2: negative active material layer

[0021] 3: flame-retardant polymer layer

[0022] 4: oxygen barrier layer

[0023] 5: oxygen

[0024] 6: pore

[0025] 7: pore clogging

[0026] 100: negative electrode

[0027] 200: lithium secondary battery

[0028] 201: case

[0029] 300: battery pack

[0030] 400: vehicle DETAILED DESCRIPTION

[0031] Hereinafter, the present specification will be described in more detail.

[0032] <DEFINITIONS>

[0033] Before describing the present application, some terms will be defined first.

[0034] When a part "comprises" a constitutional element in the present specification, unless otherwise specifically described, this does not mean to exclude another constitutional element, but means that another constitutional element can be further included.

[0035] In the present specification, "p to q" means a range of "p or more and q or less".

[0036] In the present specification, (meth)acrylate means both acrylate and methacrylate.

[0037] In the present specification, the fact that a polymer contains a monomer as a monomer unit means that the monomer participates in a polymerization reaction and is thus included in the polymer as a repeating unit. In the present specification, when a polymer contains a monomer, it is interpreted to be the same as when the polymer contains a monomer as a monomer unit.

[0038] In the present specification, "polymer" is understood to be used in a broad sense, including copolymer, unless otherwise specified as "homopolymer".

[0039] In the present specification, "copolymer" can be block copolymer, alternating copolymer, random copolymer, or graft copolymer, and is not particularly limited.

[0040] In the present specification, "monomer unit" means a state in which a compound is polymerized and incorporated in a polymer.

[0041] In the present specification, weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-conversion molecular weights measured by gel permeation chromatography (GPC) using a commercially available monodisperse polystyrene polymer (standard sample) having different polymerization degrees as a standard substance for molecular weight measurement. In the present specification, unless otherwise described, molecular weight means weight average molecular weight.

[0042] Weight average molecular weight is one of average molecular weights in which molecular weights are not uniform and a molecular weight of any polymer material is used as a reference, and is a value obtained by averaging molecular weights of component molecular species of a polymer compound having a molecular weight distribution by weight fraction.

[0043] Weight average molecular weight can be measured by gel permeation chromatography (GPC) analysis.

[0044] Hereinafter, examples of the present application will be described in detail with reference to the accompanying drawings, so that those skilled in the art to which the present application pertains can easily practice the present application. However, the present application can be implemented in various different forms and is not limited to the exemplary embodiments described herein.

[0045] <surface protective film>

[0046] The surface protective film according to one example embodiment of the present specification is characterized in that the indentation depth measured by Method 1 is 3.0 μm or more.

[0047] Specifically, Method 1 is a method in which the indentation depth of the adhesive film is measured using a special nanoindenter under conditions of a specific indentation speed and force in a state in which a glass substrate is provided on the surface of the base film opposite to the surface in contact with the adhesive film.

[0048] For the surface film according to the example embodiment, the unseparation rate can be improved by measuring the indentation depth to grasp the unseparation rate in advance, and thus, the chip defect rate can be effectively reduced.

[0049] In another example embodiment of the present invention, the adhesive film can be converted to have a ratio of the indentation depth to the total thickness of the adhesive film of 2% or more, 2.3% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, and 15% or more as measured by Method 1.

[0050] Figures 3 to 5 is a view of a mechanism in which chip separation occurs, Figure 3 is a schematic view of a stealth dicing and grinding (grinding process), and describes a process in which the surface protective film is brought into contact with one surface of the wafer subjected to the stealth dicing and a grinding process is performed on the back surface of the contacted surface, Figure 4 describes a process in which separation occurs due to deformation under pressure based on the entire wafer due to the wafer portion subjected to the grinding process being pressurized and the wafer portion not subjected to the grinding process not being pressurized (unpressurized region), and Figure 5 describes separation occurring between the pressurized region and the unpressurized region.

[0051] According to one example embodiment of the present specification, a surface protective film includes a base film and an adhesive film on one surface of the base film, and the adhesive film 1 and the base film 2 are sequentially stacked in Figure 1 .

[0052] According to one example embodiment of the present specification, the adhesive film can include an adhesive composition or a cured product thereof.

[0053] In the present specification, the adhesive composition is a composition in a state before curing, and can mean a uniform mixture including two or more substances.

[0054] In the present specification, the cured product can mean a product cured by heat and / or light (UV).

[0055] In one exemplary embodiment of this specification, the adhesive composition may comprise a (meth)acrylate-based resin and a polyisocyanate.

[0056] In this specification, the term "(meth)acrylate" is used to refer to both acrylates and methacrylates.

[0057] In one exemplary embodiment of this specification, the (meth)acrylate-based resin may comprise a copolymer of (meth)acrylate alkyl ester monomers and monofunctional or polyfunctional (meth)acrylate monomers.

[0058] In one exemplary embodiment of this specification, the monofunctional or polyfunctional (meth)acrylate monomer includes a hydroxyl-containing (meth)acrylate monomer and may contain a polyisocyanate in an amount of 60 mol% or more and 80 mol% or less relative to the total amount of the hydroxyl-containing (meth)acrylate monomer.

[0059] In this specification, (meth)acrylate containing hydroxyl groups means a substance in which the hydroxyl group is attached to a portion that can be bonded to the (meth)acrylate.

[0060] In one exemplary embodiment of this specification, the content of the hydroxyl-containing (meth)acrylate can be adjusted in the desired amount if desired, such that (meth)acrylate units are formed at both ends of the oligomer.

[0061] Examples of hydroxyl-containing (meth)acrylates in this specification include, but are not limited to, 2-HEA, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate.

[0062] When the above composition and content are met, the physical properties required for adhesive films used for surface protection films (especially adhesive tapes for processing semiconductor wafers) can be achieved, such as excellent ability to absorb irregularities and warpage tolerance, and the content of polyisocyanates and melting temperature (Tm) can be controlled.

[0063] In one exemplary embodiment of this specification, the adhesive composition further comprises an additive, and the additive may be selected from polymerization initiators, curing agents, and molecular weight modifiers.

[0064] In this specification, based on 100 parts by weight of the adhesive composition, the polymerization initiator may be used in the range of 0.01 parts by weight to 2 parts by weight, but is not particularly limited thereto.

[0065] In this specification, the polymerization initiator may be a thermal polymerization initiator, a photopolymerization initiator, or a combination thereof.

[0066] There are no particular limitations on the thermal polymerization initiator, as long as it is known in the art, but it can be selected from peroxide-based initiators, azo-based initiators, etc., and can be, for example, azobisisobutyronitrile (AIBN).

[0067] There are no particular restrictions on photopolymerization initiators, as long as they are known in the art.

[0068] In this specification, a molecular weight regulator, also known as a polymerization inhibitor, is a substance that can be used as a chain transfer agent during the free radical polymerization of a polymer, and whose molecular weight, particle size, etc., can be adjusted according to its concentration. Examples of molecular weight regulators include, but are not limited to, n-dodecyl mercaptan (n-DDM) and S,S-dibenzyl trithiocarbonate.

[0069] In one exemplary embodiment of this specification, the weight-average molecular weight (MW) of the (meth)acrylate-based resin may be 500,000 g / mol or greater and 5,000,000 g / mol or less.

[0070] In one exemplary embodiment of this specification, the thickness of the adhesive film may be 10 μm or greater and 40 μm or less.

[0071] In another exemplary embodiment of this specification, the thickness of the adhesive film may be 15 μm or greater, or 20 μm or greater, and 35 μm or less, or 30 μm or less.

[0072] When the thickness of the adhesive film falls within the above range, the proportion of air bubbles generated in the adhesive film can be reduced, and therefore, the adhesive film has the characteristics of excellent adhesive strength when adhered to the substrate and no lifting phenomenon, and no denting problem.

[0073] According to an exemplary embodiment of the present invention, the glass transition temperature (Tg) of the (meth)acrylate-based resin can be -80°C or higher and -30°C or lower.

[0074] Specifically, the glass transition temperature of the (meth)acrylate-based resin can be -80°C or higher and -30°C or lower, more specifically -75°C or higher and -40°C or lower.

[0075] Surface protective films based on (meth)acrylate resins with glass transition temperatures within the above range can achieve excellent chip separation performance and can realize appropriate physical properties for adhesive films used as surface protective films for future semiconductors.

[0076] Based on 100 parts by weight of the (meth)acrylate-based resin, the content of the curing agent may be 0.1 parts by weight or more and 1.5 parts by weight or less.

[0077] Specifically, based on 100 parts by weight of the (meth)acrylate-based resin, the content of the curing agent may be 0.1 parts by weight or more and 1.5 parts by weight or less, 0.2 parts by weight or more and 1.2 parts by weight or less, or 0.3 parts by weight or more and 1.0 parts by weight or less.

[0078] With the above-mentioned range, the surface protective film can have high peel strength before the adhesive film is irradiated with light, which enables it to perform well in protecting the semiconductor surface during the polishing process, and the chip separation characteristics during polishing can be excellent.

[0079] According to an exemplary embodiment of the present invention, the (meth)acrylate-based resin included in the composition for forming an adhesive film (adhesive composition) can be a reaction product of a (meth)acrylate-based copolymer and a (meth)acrylate containing isocyanate groups. The adhesive composition may also include a polymerization initiator and a curing agent as additives.

[0080] According to an exemplary embodiment of the present invention, the weight-average molecular weight of the (meth)acrylate-based resin can be from about 300,000 g / mol to about 1,500,000 g / mol.

[0081] By having a weight-average molecular weight within the above range, the adhesive composition can ensure appropriate viscosity and uniform coatability when forming an adhesive film during the preparation of a surface protective film.

[0082] According to an exemplary embodiment of the present invention, the (meth)acrylate-based copolymer can be copolymerized from a mixture of (meth)acrylate monomers comprising alkyl-containing (meth)acrylate monomers and hydroxyl-containing (meth)acrylate monomers.

[0083] According to an exemplary embodiment of the present invention, the (meth)acrylate-based copolymer can be copolymerized from a mixture of (meth)acrylate monomers comprising: a first (meth)acrylate monomer containing an alkyl group having 5 to 10 carbon atoms; a second (meth)acrylate monomer containing an alkyl group having 1 to 4 carbon atoms; and a third (meth)acrylate monomer containing a hydroxyl group.

[0084] Specifically, the first (meth)acrylate monomer containing an alkyl group having 5 to 10 carbon atoms may include at least one of the following: n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isohexyl methacrylate, n-heptyl methacrylate, isoheptyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, ethylhexyl methacrylate, n-nonyl methacrylate, isononyl methacrylate, n-decyl methacrylate, and isodecyl methacrylate.

[0085] Specifically, the second (meth)acrylate monomer containing an alkyl group having 1 to 4 carbon atoms may include at least one of the following: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and tert-butyl (meth)acrylate.

[0086] Specifically, the third hydroxyl-containing (meth)acrylate monomer may include at least one of the following: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 2-hydroxyethylene glycol (meth)acrylate, and 2-hydroxypropylene glycol (meth)acrylate.

[0087] According to an exemplary embodiment of the present invention, the (meth)acrylate monomer mixture may comprise 50 to 75 parts by weight of a first (meth)acrylate monomer, 0 to 15 parts by weight of a second (meth)acrylate monomer, and 25 to 45 parts by weight of a third (meth)acrylate monomer.

[0088] According to an exemplary embodiment of the present invention, the (meth)acrylate containing an isocyanate group may include at least one of 2-methacryloyloxyethyl isocyanate (MOI) and 2-acryloyloxyethyl isocyanate (AOI).

[0089] According to an exemplary embodiment of the present invention, based on 100 mol% of a third hydroxyl-containing (meth)acrylate monomer, the content of the isocyanate-containing (meth)acrylate can be 30 mol% or more and 70 mol% or less, or 35 mol% or more and 65 mol% or less. When the surface protective film has the content within the above range, the crosslinking reaction is fully carried out by light irradiation, thereby reducing the peel strength.

[0090] According to an exemplary embodiment of the present invention, the thickness of the adhesive film is 10 μm or greater and 30 μm or less. Specifically, the thickness of the adhesive film can be 15 μm or greater and 35 μm or less, or 20 μm or greater and 30 μm or less. By having a thickness within the above range, the tape used to protect the semiconductor surface can maintain adhesion to the adherend.

[0091] According to an exemplary embodiment of the present invention, the peel strength of the adhesive film relative to the wafer surface at 25°C can be 1000 gf / inch or greater, and after irradiation with light of 0.5 J energy, the peel strength relative to the wafer surface at 25°C can be 30 gf / inch or less. With peel strength relative to the wafer surface within the aforementioned range, the surface adhesive film adheres well to the semiconductor surface during the polishing process, effectively preventing damage and deformation of semiconductor circuits, etc., and when the surface protective film is peeled off after the polishing process, the peel strength is reduced by light irradiation, allowing the surface protective film to be easily peeled off from the semiconductor surface.

[0092] According to an exemplary embodiment of the invention, the peel strength of the adhesive film relative to the wafer surface can be 1000 gf / inch or greater. Furthermore, after light irradiation, the peel strength of the adhesive film relative to the wafer surface can be 30 gf / inch or less. When the adhesive film has a peel strength within the above range, it can skillfully perform the function of protecting the semiconductor surface during the polishing process, and after the polishing process, the peel strength is reduced by light irradiation, allowing the adhesive film to be easily peeled off without damaging the semiconductor surface.

[0093] In one exemplary embodiment of this specification, the base membrane may be selected from polyethylene terephthalate membranes, polyethylene naphthalate membranes, polybutylene terephthalate membranes, polyolefin membranes, polyvinyl chloride membranes, polyurethane membranes, ethylene-vinyl acetate copolymer membranes, ethylene-alkyl acrylate copolymer membranes, and combinations thereof, but there are no particular limitations as long as they correspond to a rigid base, and may further exemplify polyesters (e.g., fully aromatic polyesters), polyamides, polyimides, polycarbonates, polyacetals, modified polyphenylene ethers, polyphenylene sulfides, polysulfones, polyetherketones, biaxially oriented polypropylene, etc.

[0094] In one exemplary embodiment of this specification, a hard coating may also be included on the surface of the base film opposite to the surface in contact with the adhesive film. (See also...) Figure 2 The adhesive film 1, the base film 2, and the hard coating 3 are stacked in this order.

[0095] By further providing a hard coating, the surface protective film according to an exemplary embodiment of the present invention can prevent the base film from being contaminated and / or damaged by external factors, and can protect the surface of the base film until it is attached to the wafer surface and used.

[0096] In one exemplary embodiment of this specification, a release film may also be included on the surface of the adhesive film opposite to the surface in contact with the base film. (See reference...) Figure 2 Release film 4 is stacked on the surface of adhesive film 1 opposite to the surface of base film 2.

[0097] By further providing a release film, the surface protective film according to an exemplary embodiment of the present invention can prevent the adhesive film from being contaminated and / or damaged by external factors, and can protect the surface of the adhesive film until it is attached to the wafer surface and used.

[0098] In one exemplary embodiment of the present invention, the release film may be a polyethylene terephthalate film, a polyolefin film, an ethylene-vinyl acetate film, a polybutylene terephthalate film, a polypropylene film, or a polyethylene film, but the type of release film is not limited thereto.

[0099] In this specification, the base membrane 2 may be subjected to antistatic treatment.

[0100] In this specification, the thickness of the base membrane 2 may be 25 μm or greater, or 50 μm or greater and 150 μm or less, or 125 μm or less.

[0101] When the thickness of the base film 2 falls within the above range, the stacked surface protective film 100 has the characteristic of being able to be thinned and has the characteristic of being able to fully protect the adhered object from external impact when applied to subsequent processes.

[0102] Reference Figure 2 The surface protective film 100 is formed by stacking the adhesive film 1 and the base film 2 in this order, and the release film 4 is stacked on the surface of the adhesive film 1 opposite to the surface of the base film 2.

[0103] In this specification, hydrophobic films can be used as release films. A release film is a layer used to protect an adhesive sheet with a very small thickness and refers to a transparent layer attached to one surface of the adhesive film. Films with excellent mechanical strength, thermal stability, moisture barrier properties, and isotropy can be used. For example, acetate-based resin films (e.g., triacetyl cellulose (TAC)), polyester-based resin films, polyethersulfone-based resin films, polycarbonate-based resin films, polyamide-based resin films, polyimide-based resin films, polyolefin-based resin films, cycloolefin-based resin films, polyurethane-based resin films, acrylic resin films, etc., can be used. However, the release film is not limited to these, as long as it is a commercially available silicone-treated release sheet. When used to protect surfaces used in a process, the release film can be completely removed.

[0104] In this specification, the thickness of the release film may be 10 μm or greater, 12 μm or greater, or 15 μm or greater, or 100 μm or less, 75 μm or less, or 50 μm or less.

[0105] Reference Figure 1 and Figure 2 An antistatic layer may also be included on the surface of the base film 2 that is in contact with the adhesive film 1.

[0106] In this specification, the term "antistatic layer" refers to a layer designed to suppress the generation of static electricity.

[0107] The adhesive film 1 can be disposed on one surface of the antistatic layer to reduce the amount of accumulated static electricity. Furthermore, since the surface resistance of the adhesive film 1 is reduced, the generation of static electricity on the surface of the adhesive film can be further reduced when the protective layer is peeled off from the surface protective film 100.

[0108] Therefore, when the protective layer is removed from the surface protective film, or when the surface protective film is peeled off from the surface of the adherend to attach the adhesive film 1 to the surface of the adherend, foreign matter that can be electrostatically attached to the adhesive film or the adherend can be prevented. Furthermore, by preventing contamination of the surface of the adherend during the process, the deterioration of the surface properties of the adherend can be further prevented.

[0109] The antistatic layer can be formed using known methods to achieve the desired effect. For example, the antistatic layer can be formed on one or both surfaces of the base film using an in-line coating method.

[0110] In this invention, it is conceivable that the purpose of this application is to form an antistatic layer from a suitable antistatic composition. For example, the antistatic layer may comprise, but is not limited to, one selected from acrylic resins, urethane-based resins, urethane-acrylic copolymers, ester-based resins, ether-based resins, amide-based resins, epoxy-based resins, and melamine resins.

[0111] In one example, the antistatic layer may contain a conductive material. The conductive material may include, but is not limited to, conductive polymers or carbon nanotubes.

[0112] Conductive polymers may include, for example, polymers based on polyaniline, polymers based on polypyrrole, polymers based on polythiophene, derivatives thereof, or copolymers thereof, but are not limited thereto.

[0113] Carbon nanotubes can have a tubular form created by winding graphite sheets, which are formed by connecting hexagonal rings consisting of six carbon atoms each. Carbon nanotubes exhibit excellent rigidity and conductivity, which allows for increased hardness and improved antistatic properties when used as an antistatic layer in a surface protective film.

[0114] The thickness of the antistatic layer can be appropriately selected if needed, and the thickness of the antistatic layer can be 10 nm or greater; or 20 nm or greater. In an exemplary embodiment, the thickness of the antistatic layer can be 400 nm or less, 300 nm or less, or 100 nm or less. When the thickness of the antistatic layer is 10 nm or greater and 400 nm or less, the antistatic layer can have excellent coatability to the base film.

[0115] <Methods for evaluating adhesive films>

[0116] A method for evaluating an adhesive film according to an exemplary embodiment of this specification includes measuring the indentation depth by method 1.

[0117] [Method 1]

[0118] Indentation depth refers to the depth measured when a glass substrate is placed on the surface of the base film opposite to the surface in contact with the adhesive film, using a nanoindenter with a hemispherical tip of 2 mm in diameter at one end, applying a force of 5 mN to the adhesive film at an indentation speed of 0.25 mN / s, and then holding the 5 mN force for 5 seconds.

[0119] In the measurement method described in Method 1 above, when the indentation depth is 3.0 μm or greater, or when the value converted to the ratio of indentation depth to the total thickness of the adhesive film is 2% or greater, 2.3% or greater, 3% or greater, 4% or greater, 5% or greater, 6% or greater, 7% or greater, 8% or greater, 9% or greater, 10% or greater, 11% or greater, 12% or greater, 13% or greater, 14% or greater, and 15% or greater, it can provide the effect of reducing the non-separation rate.

[0120] Furthermore, the matters described above regarding the surface protective film can be applied to this exemplary embodiment.

[0121] Invention Embodiments

[0122] In the following description, this specification will be described in detail with reference to embodiments used to specifically describe this specification. However, various modifications may be made to the embodiments described herein, and these modifications should not be construed as limiting the scope of this specification to the embodiments described below. The embodiments of this specification are provided to illustrate this specification more completely to those skilled in the art.

[0123] <Preparation Example> Preparation of an adhesive composition comprising a (meth)acrylate-based resin

[0124] After adding ethylhexyl acrylate (EHA) / methyl acrylate (MA) / hydroxyethyl acrylate (HEA) in a weight ratio of 65:0:35 (molecular weight 1,000,000 g / mol, MOI modification 50%) to ethyl acetate (EA), azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator to prepare the (meth)acrylate-based resin of Preparation Example 1 with a weight average molecular weight of 1,000,000 g / mol, and its glass transition temperature is shown in Table 1 below.

[0125] In addition, Preparation Examples 2 and 3 were prepared according to the composition and content (based on weight ratio) shown in Table 1 below.

[0126]

[0127] Then, 70 mol% of 2-methacryloyloxyethyl isocyanate (MOI) based on HEA is added, and the resulting mixture is stirred for 24 hours or longer to prepare the adhesive composition.

[0128] <Examples 1 to 3 and Comparative Examples 1 and 2>

[0129] Preparation of surface protective film

[0130] After adding 0.4 parts by weight of an isocyanate-based curing agent (MHG-80B, Asahi Kasei Corporation) and 3 parts by weight of a photoinitiator (Irgacure 184) to 100 parts by weight of the solid contents of the (meth)acrylate resin prepared in Preparation Examples 1 to 3, methyl ethyl ketone (MEK) solvent was added thereto, so that the solid content became 30%, thereby preparing an adhesive composition (a composition for forming an adhesive film).

[0131] Subsequently, the adhesive composition was applied to one surface of a base film (PET film) with a thickness of 100 μm, and then dried in an oven at 120°C for 2 minutes to form an adhesive film with a thickness of 25 μm. Then, a release film was laminated to the other surface of the adhesive film to prepare the surface protective films of Examples 1 to 3 and Comparative Examples 1 and 2 in Table 2 below.

[0132] Each surface protective film is aged in an oven at 50°C for two days or more.

[0133] <Experimental Example>

[0134] 1. Sample preparation

[0135] After cutting the surface protective films of Examples 1 to 3 and Comparative Examples 1 and 2 into 10 cm × 10 cm sizes, the release film was removed, and then the adhesive film was fixed to the glass plate with the exposed surface facing up, thereby preparing the sample.

[0136] 2. Experimental Example 1: Measurement of Indentation Depth

[0137] The indentation depth of the specimen with the surface protective film fixed on the glass plate was measured using a nanoindenter (MH-2000 manufactured by Helmut Fischer).

[0138] The indentation depth is determined by the following method 1.

[0139] [Method 1]

[0140] Indentation depth refers to the depth measured when a glass substrate is placed on the surface of the base film opposite to the surface in contact with the adhesive film, using a nanoindenter with a hemispherical tip of 2 mm in diameter at one end, applying a force of 5 mN to the adhesive film at an indentation speed of 0.25 mN / s, and then holding the 5 mN force for 5 seconds.

[0141] 3. Experimental Example 2: Measurement of Non-Separation Rate

[0142] A surface protective film is attached to the circuit surface of a 12-inch wafer with a thickness of 750 μm on which circuitry is formed.

[0143] After stealth dicing, the wafer is ground to a final thickness of 50 μm, and then the unseparated ratio is calculated.

[0144] The unseparation rate refers to the average value obtained by measuring the unseparation rate of four wafers for each type of film. When the average unseparation rate is 0.1% or greater, it is evaluated as NG, while when the average unseparation rate is less than 0.1%, it is evaluated as OK.

[0145] 4. Experimental Example 3: Measurement of Peel Strength

[0146] The adhesive film of the surface protective film is attached to a stainless steel substrate by rolling it back and forth once with a 2 kg rubber roller, and then the film is left to stand at 23°C for 30 minutes or longer.

[0147] Then, the initial peel strength of the adhesive film of the surface protective film was measured (before UV) using a texture analyzer (Stable Micro Systems) at a peel angle of 180° and a peel speed of 1800 mm / min.

[0148] Subsequently, the adhesive film of the surface protective film was irradiated with light of 0.5 J to further cure it, and the peel strength was measured later (after UV).

[0149] The results of Experiments 1 to 3 are shown in Table 2 below.

[0150]

[0151] According to Table 2 above, the surface protective films of Comparative Examples 1 and 2, with indentation depths less than 3.0 μm, were found to have excellent peel strength, but a non-separation rate greater than 0.15%, while the surface protective films of Examples 1 to 3, with indentation depths of 3.0 μm or greater, had a non-separation rate of less than 0.1%, showing an improvement in non-separation rate, while maintaining excellent peel strength. Therefore, by determining the relationship between indentation depth and non-separation rate, as measured by applying the nanoindentation technique according to this specification to the adhesive film of the surface protective film (i.e., Method 1), it can be determined that this is useful for improving the non-separation rate.

Claims

1. A surface protective film comprising a base film; and an adhesive film on one surface of the base film, The indentation depth of the adhesive film, as measured by method 1, is 3.0 μm or greater. [Method 1] The indentation depth refers to the depth measured when a glass substrate is disposed on the surface of the base film opposite to the surface in contact with the adhesive film, using a nanoindenter with a hemispherical tip of 2 mm in diameter at one end, applying a force of 5 mN to the adhesive film at an indentation speed of 0.25 mN / s, and then holding the 5 mN force for 5 seconds.

2. The surface protective film according to claim 1, wherein the adhesive film comprises an adhesive composition or a cured product thereof.

3. The surface protective film according to claim 2, wherein the adhesive composition comprises a (meth)acrylate-based resin and a polyisocyanate.

4. The surface protective film according to claim 3, wherein the glass transition temperature (Tg) of the (meth)acrylate-based resin is -80°C or higher and -30°C or lower.

5. The surface protective film according to claim 3, wherein the (meth)acrylate-based resin comprises a copolymer of an alkyl (meth)acrylate monomer and a monofunctional or polyfunctional (meth)acrylate monomer.

6. The surface protective film according to claim 5, wherein the monofunctional or polyfunctional (meth)acrylate monomer comprises a (meth)acrylate monomer containing a hydroxyl group, and The polyisocyanate comprising 60 mol% or more and 80 mol% or less of the total amount of the hydroxyl-containing (meth)acrylate monomer.

7. The surface protective film according to claim 2, wherein the adhesive composition further comprises additives, and The additives are selected from polymerization initiators, curing agents, and molecular weight regulators.

8. The surface protective film according to claim 3, wherein the weight-average molecular weight (MW) of the (meth)acrylate-based resin is 500,000 g / mol or greater and 5,000,000 g / mol or less.

9. The surface protective film according to claim 1, wherein the thickness of the adhesive film is 10 μm or greater and 40 μm or less.

10. The surface protective film according to claim 1, wherein the base film is selected from polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyolefin film, polyvinyl chloride film, polyurethane film, ethylene-vinyl acetate copolymer film, ethylene-alkyl acrylate copolymer film, and combinations thereof.

11. The surface protective film of claim 1, further comprising a hard coating on the surface of the base film opposite to the surface in contact with the adhesive film.

12. The surface protective film according to claim 1, further comprising a release film on the surface of the adhesive film opposite to the surface in contact with the base film.

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